Vaporization and cracker cell method and apparatus

ABSTRACT

A method and apparatus for vaporizing and cracking chemical elements for use in a deposition process. The apparatus includes a vaporization cell integrally connected with a thermal cracker cell. The vaporization cell has an inlet section in communication with a valve section defining a heating chamber capable of holding a liquid or solid chemical material to be vaporized. A heat source is positioned in the heating chamber and is capable of providing sufficient thermal energy to evaporate or sublimate the chemical material. The thermal cracker cell is communicatively connected to an outlet of the vaporization cell, and includes an elongated tapered tube with a heating element associated therewith. The heating element is capable of providing sufficient thermal energy to dissociate molecular clusters of vaporized chemical material. This provides monomeric or dimeric chemical elements for use in a deposition process such as during semiconductor device fabrication.

[0001] This is a divisional application of U.S. patent application Ser.No. 09/241,805, filed on Feb. 2, 1999, which is incorporated herein byreference.

[0002] The U.S. Government has a paid-up license in this invention andthe right in limited circumstances to require the patent owner tolicense others on reasonable terms as provided for by the terms of GrantNo. ECS-9502891 awarded by the National Science Foundation (NFL).

BACKGROUND OF THE INVENTION

[0003] 1. The Field of the Invention

[0004] The present invention relates generally to an apparatus andmethod for transforming chemical elements from a solid state to agaseous state. More specifically, the present invention relates to anapparatus and method for vaporizing and cracking chemical elements foruse in a deposition process such as during semiconductor devicefabrication.

[0005] 2. The Relevant Technology

[0006] Various chemical elements are used in conventional depositionprocesses performed during semiconductor device fabrication. Forexample, the chemical elements in Group V of the periodic table, such asphosphorus and arsenic, are commonly used as dopants in semiconductorprocessing technologies and are vital materials in several semiconductordevices. It is desirable to be able to convert the solid forms of thesechemical elements into a form which may be subsequently combined withother chemical elements to create the desired product. To accomplishthis, the chemical elements must first be vaporized.

[0007] Conventional techniques for converting chemical elements intovapor phase for semiconductor device fabrication employ a vacuumevaporation system. Generally, the vacuum evaporation system includes aheating unit and is in communication with a growth chamber fordeposition of the element onto a substrate. The heating unit is used tosupply the required energy to convert the element into a vaporous form,and the growth chamber is ideally operated under high vacuum conditions,as this ensures a high quality, non-contaminated crystal. One techniquethat employs such a vacuum evaporation system is molecular-beam epitaxy(MBE).

[0008] In MBE, a variety of sources can be employed for flux generation,and their design depends on the nature of source materials. The thermaleffusion source or Knudsen-cells (kcells) are used in nearly all MBEsystems for deposition of semiconductor and/or dopant materials duringsemiconductor device fabrication. A k-cell includes a cruciblecontaining a solid or liquid evaporant, which is radiatively heated byelectrically insulated heater filaments wound around the crucible. Athermocouple, which is carefully positioned to ensure intimate contactwith the crucible, registers the source material temperature and can,via a feed-back loop, control the power to the heater and thus thetemperature of the source. Several layers of refractory metal foil(e.g., tantalum) are wrapped around the entire cell to minimize heatlosses from the cell wall, with the major heat loss being from theeffusion aperture.

[0009] Typically, the vaporization process yields varying ratios ofchemical elements in monomeric, dimeric, and tetrameric forms.Conventional vaporization techniques for group V elements are unable toreduce the majority of the element to a monomeric or dimeric form,resulting in a substantial amount of tetrameric forms of the element.Such tetrameric forms of group V elements are undesirable from thestandpoint of use in semiconductor device fabrication. The growth of acrystalline layer, which is required for semiconductor deviceapplications, is best achieved when the monomeric (atomic) or thedimeric form of the element is used. Therefore, after vaporization ofthe chemical element, a method to efficiently convert clusters oftetrameric forms of the element into monomeric and dimeric forms is ofsubstantial interest.

[0010] Several techniques for converting or “cracking” tetrameric formsof chemical elements into monomeric or dimeric forms have beendeveloped. Such techniques employ either extremely high temperatures orultraviolet light to input the energy necessary to separate elementalclusters. Some of these systems, such as the ultraviolet light systems,are very mechanically complex with many small parts requiring continualadjustments in order to achieve optimal performance. For example,precise alignment of parts is necessary to focus an ultraviolet beam ina manner that will achieve efficient cracking of elemental clusters.

[0011] The disadvantages of cracking systems that employ extreme heat orultraviolet light include the high maintenance and expense required torun and maintain such systems. The high expense is incurred through boththe power consumption and the mechanical maintenance required. Inaddition, most known systems for evaporating and cracking chemicalelements have separate evaporation and cracker cell units, which reducesthe efficiency of providing the chemical elements in a desirable formfor deposition.

[0012] It would therefore be of significant advantage to develop asimple, inexpensive, and efficient system which can perform both thefunctions of chemical element vaporization and cracking.

SUMMARY AND OBJECTS OF THE INVENTION

[0013] It is an object of the present invention to provide an apparatusfor vaporizing and cracking chemical elements for use in a depositionprocess during semiconductor device fabrication.

[0014] It is another object of the present invention to provide such avaporizing and cracking apparatus that is simple in design andmanufacture, and inexpensive to use and maintain.

[0015] It is another object of the present invention to provide such avaporizing and cracking apparatus which is a fully integrated orcombined effusion system.

[0016] It is a further object of the present invention to provide such avaporizing and cracking apparatus which is easy to use and operates atpeak efficiency.

[0017] To achieve the foregoing objects, and in accordance with theinvention as embodied and broadly described herein, an apparatus isprovided for vaporizing and cracking chemical elements such as group Velements for use in a deposition process. The apparatus includes avaporization cell integrally connected with a thermal cracker cell.

[0018] The vaporization cell has an inlet section in communication witha valve section defining a heating chamber capable of holding a chemicalmaterial to be evaporated or sublimated. A container such as a quartzboat is preferably disposed in the heating chamber for holding thechemical material. A heat source is positioned in the heating chamberand is capable of providing sufficient thermal energy to evaporate orsublimate the chemical material.

[0019] The thermal cracker cell is communicatively connected to anoutlet of the vaporization cell, and includes a tapered elongated tubewith a heating element such as a heating coil disposed therearound. Theheating element is capable of providing sufficient thermal energy todissociate molecular clusters of vaporized chemical material. Thisprovides monomeric or dimeric chemical elements for use in a depositionprocess. The elongated tube is preferably composed of quartz and has apassageway with a diameter of a first dimension that narrows to asmaller second dimension toward an exit opening of the tube. The tubenarrows in order to cause the gaseous clusters of elements to beseparated so that the clusters can receive a greater amount of heatenergy as a result of increased exposure to and decreased distance fromthe heating element. This exposure results in greater efficiency inseparating elemental clusters, and allows the use of lower temperatures.

[0020] In a method for vaporizing and cracking a chemical material whichutilizes the apparatus of the invention, a preselected amount of achemical material is placed into the heating chamber, and the chemicalmaterial is heated to a first temperature sufficient to vaporize thechemical material. The temperature in the heating chamber can bemonitored and adjusted for optimal vaporizing conditions. The vaporizedchemical material is then directed to the elongated tube and is heatedalong the smaller second dimension of the passageway in the elongatedtube to a higher second temperature sufficient to dissociate molecularclusters of vaporized chemical material. The dissociated chemicalmaterial can then be directed from the exit opening of the elongatedtube to a vacuum chamber for deposition on a substrate.

[0021] These and other objects, features, and advantages of the presentinvention will become more fully apparent from the following descriptionand appended claims, or may be learned by the practice of the inventionas set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more fully understand the manner in which theabove-recited and other advantages and objects of the invention areobtained, a more particular description of the invention brieflydescribed above will be rendered by reference to a specific embodimentthereof which is illustrated in the appended drawings. Understandingthat these drawings depict only a typical embodiment of the inventionand are not therefore to be considered limiting of its scope, theinvention will be described and explained with additional specificityand detail through the use of the accompanying drawings in which:

[0023]FIG. 1 is a side view of an vaporization and cracker cellapparatus according to the present invention; and

[0024]FIG. 2 is a cross-sectional view of the vaporization and crackercell apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention is directed to an apparatus and method forvaporizing and cracking chemical elements such as group V elements. Theinvention is particularly useful in deposition processes such as thoseemployed during semiconductor device fabrication. The apparatus of theinvention provides an efficient, simple, and economic way of performingboth chemical element vaporization and cracking during a depositionprocess such as MBE.

[0026] The apparatus of the invention provides for a two-step heatingprocess in which a chemical material in a solid or liquid state is firstvaporized and then further heated to crack or dissociate vaporousmolecular clusters into monomeric or dimeric forms of a chemicalelement. As used herein, the term “monomeric” refers to the atomic formof any element or a single atom of any element unbound to other atoms ofthe same element, while the term “dimeric” refers to two atoms of anyelement which are bonded to one another.

[0027] Referring to the drawings, wherein like structures are providedwith like reference designations, the drawings only show the structuresnecessary to understand the present invention. FIG. 1 illustrates avaporization and cracker cell apparatus 10 according to the presentinvention. The apparatus 10 is shown operatively connected at one end toa power source 12 and a control device 14, which will be discussed infurther detail below in connection with the operation of apparatus 10.The outlet end of apparatus 10 is in communication with a vacuum chamber16 where deposition of a material from apparatus 10 takes place during afabrication process. The apparatus 10 as a whole can be fitted onto anyvacuum chamber by choosing components of appropriate dimension, as fitseach individual chamber, and can operate efficiently in vacuum below themillitorr range.

[0028] The apparatus 10 includes two subunits, a vaporization cell 18and a thermal cracker cell 20, which are communicatively attachedtogether in an integral structure. Each of these subunits will bediscussed in detail as follows.

[0029] As shown in FIGS. 1 and 2, vaporization cell 18 includes an inletsection 22 and an outlet section 24 which are communicatively connectedto a valve section 26 therebetween. The inlet section 22, outlet section24, and valve section 26 are preferably hollow tubular structures whichcan be formed of various materials such as stainless steel. The inletsection 22 and outlet section 24 are preferably attached on oppositesides of valve section 26 in a parallel configuration perpendicular tovalve section 26.

[0030] The inlet section 22 has two subsections, including a valve inletportion 28 and a feedthrough section 30. The valve inlet portion 28 iscommunicatively connected at one end to valve section 26 and on theother end has a circular connection flange 32. The feedthrough section30 has a pair of opposing connection flanges 34 and 36 on each endthereof. The connection flange 34 is attached to flange 32 by aplurality of bolts 35 inserted between the flanges to provide forremovable attachment of feedthrough section 30 with valve inlet portion28. The connection flange 36 is removably attached to a feedthroughflange 38 by bolts 35, and the feedthrough flange 38 is removablyattached to a smaller guide flange 39. A sealing gasket 41 such as acopper gasket is preferably disposed between each of the attachedflanges to provide a vacuum seal. The feedthrough flange 38 and guideflange 39 have openings therein permitting insertion of a powerfeedthrough 40 and a thermocouple feedthrough 42 into inlet section 22.As shown in FIG. 1, power feedthrough 40 is operatively connected topower source 12, and thermocouple feedthrough 42 is operativelyconnected to control device 14. The power feedthroughs are individuallyfitted through the flanges to minimize the size constraints.

[0031] The valve section 26 of vaporization cell 18 is preferably anin-line manual valve which includes a tubular section 44 with a circularconnection flange 46 and a valve assembly 48 with a connection flange50. The connection flange 50 is removably attached to connection flange46 by bolts 35 inserted between the flanges. A sealing gasket 51 such asa copper gasket for vacuum seal is disposed between connection flanges46 and 50. The tubular section 44 defines a heating chamber 52, whichholds a chemical element container 54 such as a quartz boat that servesas a crucible for a chemical material 60 to be evaporated or sublimated.As depicted in FIG. 2, container 54 preferably has a handle 56 whichextends into inlet section 22, allowing for easy insertion and removalof container 54 into and from chamber 52. The container 54 is designedto hold a maximum amount of chemical material 60 to be vaporized, insolid or liquid form, without spilling during refill operations.

[0032] A heating means is provided such as a heat source 62 for raisingthe temperature of chemical material 60 to its vaporization temperature.The heat source 62 is positioned in chamber 52 adjacent to container 54and is operatively connected to power feedthrough 40. The heat source 62can be provided in the form of a light bulb, a quartz lamp, and thelike. For example, a 150 watt light bulb can be placed inside chamber 52directly above chemical material 60 held in container 54. Thethermocouple feedthrough 42, associated with a thermocouple device, isin intimate contact with container 54 through inlet section 22 andregisters the temperature of chemical material 60. The thermocoupledevice can provide, via a feed-back loop, control of the power to heatsource 62 and thus the temperature of chemical material 60.

[0033] The valve assembly 48, which can be a bellow valve assembly,includes a valve handle 64 connected to a movable bellow section 66disposed in chamber 52. The bellow section 66 terminates in a valve seat70 having an o-ring 68 for high temperature seal, such as aCalrez™o-ring. The handle 64 provides manual control such that belowsection 66 can be raised and lowered as needed during operation ofapparatus 10 in order to open or close chamber 52 with respect tocracker cell 20.

[0034] The outlet section 24 includes an outlet connection flange 72attached to a larger circular connection flange 74 by a plurality ofbolts 35 inserted between the flanges to provide for removableattachment of cracker cell 20 to vaporization cell 18. A sealing gasket73 such as a copper gasket is preferably disposed between flanges 72 and74.

[0035] The thermal cracker cell 20 includes a fitting tube 76 and anelongated heating tube 78 which are in communication with vaporizationcell 18. The fitting tube 76 has a tube connection flange 80 that isbolt connected to connection flange 74. A sealing gasket 73 ispreferably disposed between flanges 74 and 80. A passageway 82 withinfitting tube 76 is in communication with the passageway of outletsection 24. The heating tube 78 defines a passageway 84 and is removablyinterconnected with fitting tube 76. The fitting tube 76 and heatingtube 78 are interconnected by a plurality of tube fittings 86, 87 and88, which are preferably Swage-Lok metallic fittings, or the like,typically used for low pressure and high temperature applications. Thefitting tube 76 interconnects with fitting 86, while heating tube 78interconnects with fitting 88. The fitting tube 76 is preferably made ofa metallic material such as stainless steel, while heating tube 78 ispreferably made of a transparent quartz material.

[0036] The heating tube 78 defines a first larger diameter forpassageway 84 which extends into fitting 88 to accentuate the flow ofthe vapor from outlet section 24. The heating tube 78 has a taperingsection 89 that narrows abruptly such that passageway 84 has a secondsmaller diameter along the majority of tube 78 which defines a crackerzone 85 therein. The cracker zone 85 is designed to provide for multiplecollisions of molecules to maximize the probability of dissociation. Thesecond smaller diameter of passageway 84 extends to an exit opening 90at the distal end of tube 78 for effusion of the dissociated vaporizedmaterial. In one embodiment, the first larger diameter of passageway 84is about 19 mm and the second smaller diameter is about 4 mm. Thepassageway 82 in fitting tube 76 and the passageway 84 in heating tube78 are aligned for easy and efficient passage of gaseous materials fromvaporization cell 18 to cracker cell 20.

[0037] A heating element such as a heating coil 92 is wrapped around theoutside of heating tube 78 toward the distal end thereof along thesmaller diameter portion of passageway 84 defining cracker zone 85. Theheating coil 92 is electrically connected to power source 12 as shown inFIG. 1 by being coupled at a connection junction 94 with a feedthroughconnection 96, which passes through flange 74 for connection with powersource 12. The heating coil 92 can be composed of various metallicmaterials such as refractory metals including tantalum, tungsten,molybdenum, alloys or combinations thereof, and the like. A particularlypreferred material for the heating coil is tantalum.

[0038] The heating coil 92 is in close proximity to heating tube 78 andprovides the thermal energy necessary to cleave elemental molecularclusters passing through tube 78. The narrowed portion of passageway 84forming cracker zone 85 in tube 78 has the effect of spacing gaseousmolecular clusters of elements which provides increased exposure of themolecular clusters to the thermal energy provided by heating coil 92.The narrowed portion in tube 78 also has the effect of bringingmolecular clusters in closer proximity to the heat provided by heatingcoil 92. These effects allow for the cracking of molecular clusters in amore efficient manner and at a lower temperature than in prior crackingdevices.

[0039] In a method of operating vaporization and cracker cell apparatus10, a preselected amount of chemical material 60 is placed in container54, which is inserted into chamber 52 of vaporization cell 18. Theconnection flange 74 is sealingly attached to a conventional connectingflange (not shown) on an inlet of vacuum chamber 16 by bolt connectionssuch that cracker cell 20 is in communication with vacuum chamber 16.The chemical material 60 is then heated sufficiently to vaporize thechemical material. Typically, the temperature in chamber 52 is in arange from about 250° C. to about 400° C., and preferably about 300° C.,in order to vaporize the chemical material. The vaporized material isthen directed into cracker cell 20 and is further heated to a crackingtemperature by heating coil 92 while passing through cracker zone 85 inheating tube 78 to dissociate molecular clusters. The temperature incracker zone 85 is in a range from about 700° C. to about 900° C., andpreferably about 800° C., in order to dissociate the vaporized material.The dissociated molecules can then be directed to vacuum chamber 16 fordeposition on a substrate such as a semiconductor material.

[0040] The parameters used in the operation of apparatus 10, such aspower, temperature, and pressure, have the capability of being adjustedto achieve the maximum possible yield of the monomeric or dimeric formof a chemical element. Power can be controlled externally by powersource 12 and control device 14 such as a computer or other digitalcontrol device. The general power consumption for power feedthrough 40is typically less than about 100 watts for apparatus 10. The temperatureis monitored by the thermocouple device and heat source 62 provides thethermal energy for the vaporization of the chemical material. Theposition of heat source 62 and the amount of power at which it operatesare parameters which may be varied in order to achieve optimization fora given element yield. The range of partial pressures utilized duringoperation of apparatus 10 can be up to about 5×10⁻⁴ torr, and preferablyfrom about 1×10⁻⁵torr to about 1×1⁻⁴ torr. Optimization runs forapparatus 10 can be carried out with the aid of a residual gas analyzer(RGA) to determine the optimal parameters for a given chemical elementyield.

[0041] During operation of apparatus 10, it is preferred that no thermalinteraction occur between vaporization cell 18 and thermal cracker cell20. This prevents loss of control over vaporization when cracker cell 20is operated. The chemical material container 54 generally only needs tobe refilled every few months, depending on the operation frequency ofapparatus 10.

[0042] The apparatus of the present invention is particularly effectivein vaporinzing and cracking group V chemical elements such asphosphorus, arsenic, antimony, and combinations thereof. For example,the apparatus of the invention can be used to convert a solid phosphorussource (P₄) such as red phosphorus to its vapor phase, and then to crackthe vaporous phosphorus to obtain varying ratios of P₃, P₂, and P. Theapparatus of the invention provides effective control over thegeneration of a vapor such as a phosphor gas. The ratios of the desiredfinal product with respect to P₃, P₂, or P, can be adjusted by varyingthe temperature of the heating coil around the quartz tube, and the rateat which the vapor passes through the quartz tube, depending on therequirement for a given application. The control of the power for thevaporization cell and the cracker cell can provide extremely stablepartial pressures of phosphorus, with almost no noticeable fluctuations.

[0043] When arsenic is vaporized and cracked by the apparatus of theinvention, it is preferable to provide an additional heat source atvarious points around apparatus 10 to prevent condensation of thearsenic. For example, a high condensation rate of the arsenic flux canoccur at the in-line valve. The additional heat source can be in theform of conventional heating tape which can be wrapped around selectedoutside portions of apparatus 10.

[0044] The apparatus of the present invention provides many advantagesand benefits. The apparatus is a fully integrated or combined effusionsystem of vaporization and cracker cells, has a simple design, and iseasy to manufacture and use. The apparatus provides an effectiveeffusion system which combines the two functions of vaporization andmolecular dissociation. The apparatus operates at peak efficiency, iseasy to assemble and disassemble for maintenance, and is inexpensive tooperate, as compared to prior source cells. The apparatus of theinvention is particularly effective in vaporizing and cracking chemicalelements for use in deposition processes during semiconductor devicefabrication. The apparatus can also be easily upgraded for largerquantities of chemical material without any consequential change indesign.

[0045] The present invention may be embodied in other specific formswithout departing from its spirit or essential characteristics. Thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is: 1 A method for vaporizing and cracking a chemicalmaterial, comprising: providing a vaporization and cracker cellapparatus comprising a heating chamber, and a heatable elongated tube incommunication with the heating chamber, the tube having a passagewaywith a diameter of a first dimension that narrows to a smaller seconddimension toward an exit opening of the tube; placing a preselectedamount of a chemical material into the heating chamber; heating thechemical material in the heating chamber to a first temperaturesufficient to vaporize the chemical material; directing the vaporizedchemical material to the elongated tube; and heating the vaporizedchemical material along the smaller second dimension of the passagewayin the elongated tube to a higher second temperature sufficient todissociate molecular clusters of vaporized chemical material.
 2. Themethod of claim 1, further comprising directing the dissociated chemicalmaterial from the exit opening of the elongated tube to a vacuum chamberfor deposition on a substrate.
 3. The method of claim 2, wherein thesubstrate comprises a semiconductor material.
 4. The method of claim 1,wherein the chemical material comprises a solid or liquid material. 5.The method of claim 1, wherein the chemical material is selected fromthe group consisting of phosphorus, arsenic, antimony, and combinationsthereof.
 6. The method of claim 1, further comprising monitoring thetemperature in the heating chamber, and adjusting the temperature in theheating chamber for optimal vaporizing conditions.
 7. A method forvaporizing and cracking a chemical material, comprising: providing avaporization and cracker cell apparatus comprising: a vaporization cellhaving a heating chamber for holding a chemical material; a heat sourcedisposed in the heating chamber; and a thermal cracker cellcommunicatively connected to an outlet of the vaporization cell, thecracker cell including an elongated tube with a heating elementassociated therewith, the tube having a passageway with a diameter of afirst dimension that narrows to a smaller second dimension by way of atapering section in the tube, the tapering section located distallyapart from an inlet of the tube, the smaller second dimension of thetube being substantially maintained from the tapering section to an exitopening of the tube; placing a preselected amount of a chemical materialinto the heating chamber; heating the chemical material in the heatingchamber to a first temperature sufficient to vaporize the chemicalmaterial; directing the vaporized chemical material to the elongatedtube; and heating the vaporized chemical material along the smallersecond dimension of the passageway in the elongated tube to a highersecond temperature sufficient to dissociate molecular clusters ofvaporized chemical material.
 8. The method of claim 7, wherein the heatsource is a light bulb or a quartz lamp mounted within the heatingchamber.
 9. The method of claim 7, wherein the vaporization cellincludes a valve section with an in-line valve for selectively sealingthe heating chamber from the passageway in the tube.
 10. The method ofclaim 7, wherein the chemical material is held by a container in theheating chamber.
 11. The method of claim 7, further comprisingmonitoring the temperature in the heating chamber by a thermocoupledevice disposed in the vaporization cell.
 12. The method of claim 7,wherein the heating element of the cracker cell comprises a heating coildisposed around an outside surface of the tube.
 13. The method of claim7, wherein the elongated tube comprises a quartz tube.
 14. A method forvaporizing and cracking a chemical material, comprising: providing avaporization and cracker cell apparatus comprising: a vaporization cellincluding an inlet section in communication with a valve sectiondefining a heating chamber; a quartz container disposed in the heatingchamber for holding a chemical material; a heat source positioned in theheating chamber adjacent to the container; a thermal cracker cellcommunicatively and removably connected to an outlet of the vaporizationcell, the cracker cell including an elongated quartz tube having apassageway with a diameter of a larger first dimension that narrows to asmaller second dimension by way of a tapering section in the tube, thetapering section located distally apart from an inlet of the tube, thesmaller second dimension of the tube being substantially maintained fromthe tapering section to an exit opening of the tube; an in-line valvedisposed in the valve section for selectively sealing the heatingchamber from the passageway in the tube; and a heating coil disposedaround an outside surface of the tube toward the exit opening; placing apreselected amount of a chemical material into the heating chamber;heating the chemical material in the heating chamber to a firsttemperature sufficient to vaporize the chemical material; directing thevaporized chemical material to the elongated tube; and heating thevaporized chemical material along the smaller second dimension of thepassageway in the elongated tube to a higher second temperaturesufficient to dissociate molecular clusters of vaporized chemicalmaterial.
 15. The method of claim 14, further comprising monitoring thetemperature in the heating chamber by a thermocouple device disposed inthe vaporization cell.
 16. The method of claim 15, wherein thethermocouple device is operatively connected to a control device formonitoring and adjusting the temperature in the heating chamber.
 17. Themethod of claim 16, wherein the heat source is operatively connected toa power source in operative communication with the control device. 18.The method of claim 17, wherein the heating coil is electricallyconnected to the power source.
 19. The method of claim 14, wherein theexit opening of the tube is in sealing communication with a vacuumchamber.
 20. The method of claim 14, wherein the chemical material isselected from the group consisting of phosphorus, arsenic, antimony, andcombinations thereof.